Back in game keybind the /tar lightwell macro to F11 and the /targetlasttarget macro to F10, then go into key bindings an set Interact with Target to F12

I bound this to button 11 on the razer naga so when i press it i get the lightwell heal an back on target instantly

Edit: Further Testing
Also made an macro and bound it to the G3 key on a Logitech G15 keyboard.... works just as good so any type of programmable mouse or keyboard should make this doable

Be careful though, as these client-side macros external to the WoW client may violate your Terms of Service.

Edit: There are two ways that you can use the Lightwell with just clicking one button, the first is the well-known one where you hover your cursor over the shiny yellow object on the screen and press the right-clicky button on your mouse. You could try to position the cursor over the shiny object and then leave it there while you smash your IWIN button so you could just hit the right click on the mouse if you needed heals but the problem with that is if you have to move or if another player stands between you and the object your cursor is no longer positioned properly, and if someone in on top of the thing you may have to run around the room trying to find that perfect angle which will allow you to see and right-click the Lightwell. The second method does at the very least resolve this problem, but it is a trade-off solution. But in some cases it may be worth it. If you want to be able to use the Lightwell without any interruption to your dps and also be able to move and use it, all with one click, here is what you have to do:
1. Focus the Lightwell
2. Hover your mouse over the focus frame (focus frame can be moved anywhere on the screen and will never be obstructed by in game objects, you can keyboard move/strafe all you want and the cursor will still be hovering over the focus frame)
3. Have a keybind set for "Interact with Mouseover"
4. Whenever you need a heal press the button

Rather than waste a focus slot, a new program called Lightwell binder has just come out that does the 3 steps (target LW, interact with target, targetlast target) in a single press, and is probably the closest to a "use lightwell bind". I can't gurantee that it's TOS friendly or clean but it works quite well.

To everyone that needs a macro to click a lightwell for you; I hope you realise just how bad you must be to find yourselves unable to perform even the simplest of tasks. Are you clicking your way through your dps rotation? Is that why your mouse hand is so preoccupied that you can't take a second to wave it over the lightwell?

If you can't even click lightwells on your own, don't bother even setting foot in heroic raids, we're not in WOTLK anymore, Toto.

To everyone that needs a macro to click a lightwell for you; I hope you realise just how bad you must be to find yourselves unable to perform even the simplest of tasks. Are you clicking your way through your dps rotation? Is that why your mouse hand is so preoccupied that you can't take a second to wave it over the lightwell?

If you can't even click lightwells on your own, don't bother even setting foot in heroic raids, we're not in WOTLK anymore, Toto.

Have you ever tried using it when many mobs or players are near it?

There is also an intrinsic "attention cost" to lightwell; that time and attention spent in accurately hovering over lightwell could have been better spent paying attention to the boss, focusing on interrupting, targetting new adds, setting traps,. For healers, thats additional time away from the frames. For tanks, using lightwell can also risk a slower pickup of adds.

Are you trying to say there is something wrong in trying to minimize the associated costs of utilizing lightwell, so that everyone can perform their role better while still taking advantage of lightwell?

Sometimes fatties stand on the lightwell, or the boss gets moved and shoves his arm in it. I can understand the frustration with that. Interesting that there is a mod out for it - I'm just glad people actually CARE enough to find a way to click it!